Bidirectional high gain amplifier



' Dag-1,1948. Q. c. SZIKLAI 2,455,711

BIDIRECTIONAL HIGH GAIN AMPLIFIER Filed Dec. 25, 1944 Fu ma INVEN'JI. u

it is substantially short-circuited to ground at the first signalfrequency f1. Also, the anode of the second triode I3 is at relativelyhigh impedance with respect to ground at the first signal frequency fr,while it is substantially shortcircuited to ground at the second signalfrequency f2. Y .s

A source of anode energizing potential is applied across a first bypasscapacitor 21 which is connected in series with the ground connection ofthe third filter network I9 for energizing the anode of the first triode1.:.Similarlyianodewff `for example, one section of a double triode l.

voltage for the second triode' I3 is applied across a second bypasscapacitor; 29jwh'ichfis 'co niecte,div

in series with the groundv connection:l off"the` fourth filter network23.

In operation, signals of. theiirstfapplied,ifre.v

amplified in the second triode`f`I'3, are cathode- *25 coupled to thecathode of the first triodellfwhich operates as a grounded gridamplifier,V and the amplifed'output of which is derived'from the outputof the third filter network I9.l

to ground for the other of these frequencies. In effect, the output lternetworks from each of the triode sections also are employed as inputfilter networks for the next succeeding tube section.

19 frequency f1 are applied to the grid electrode of the first triodesection i, which may comprise,

."Ihecommon cathode of the double triode I is i n'groundeclV throughtheserially-connected inductor"I5 and resistor Il. The anode of a secondtriode section l of the double triode I is connectedthrough a second fibandpass filter 23, having an impedance characteristic, for example,as'shown in graph 25 of the circuit oi Figure 1,

20 tol the grid of the first triode section 3l of a second'doubleltriode 39. The commonrcathode of f the second double'vtriode 39 isgrounded through a', second inductor `III and a serially-connectedsecodresis'tor (I3. l

The anode `of the second diode sectionl 45, 'of the second double triode3S, is connected through a similar third f1 bandpass lter 41 to the gridof the first triode section 49 of a third double triode 5I. fIhecommonrcathode of the double For simple bandpass networksecompisins,forBO ltriode Slis .grounded through a third seriaiiyexample, twoinductivelyyor -capacitiyely coupled parallel tuned circuits,frsuch"asare showninthe signal input circuit of Figure 3, the applied signalfrequencies preferably shouldha'v'e 'a frequency,

ratio of at least 3 to 1 to provideithe required 35., the firstl appliedfrequency f1.

selectivity and proper loperation of the circuit. For more complex andmorehighly selective filter networks, the frequency ratio' between theapplied signals may have a lower value.` s 1 w,

Y Since the first amplier tubeifcr` each of the applied signals is acathodeV follower, andfsince the second amplifier tube ineachinstanceisa grounded grid amplifier, great stability [ofoperaconnected inductor 53 and resistor 55,. The anode ofthe secondtriode section `5'Iwof the third double triode 5I is 'connected througha similargfourth `f1 bandpass filter 59 to the 'output terminals forSimilarly, the second input frequencyjz' is applied through a fifth f2bandpass ffilter 6I, having `a vcharacteristic as illustrated in graphll@of the circuit of Figure 1, to the grid electrode `of thesecond ,triodesection. 510i the third double triodey5l. ',The anode of the firsttriode vsection .4,9 ofthe thirddouble triode 5I is connected through a.sixthfz bandpassiilter 63 to thegrid tion is obtainable with relativelyhighamplifierggsof vthe second triode sectionr of the second gain, sincethe anode currents of theltwof-,triodes vary in opposite sense while theinput and'output signals at each frequency are of the same polarity, andsubstantially no regeneration isfenc'ountered. Also, at each of theappliedsignal fre-w is substantially lsuperior tof'circuits,ernployirigvoo ing potentials are minimized. 4

The series resistor I'I.` in the common cathode circuit is optional,`and maybe required'only in instanceswherein one of the applied, Signalfrepentodes, and theeffects of variations ofenergizf quencies is,relatively low or, .includes .low frequency or D.-C.r components.

In the circuit of Figure 2, the principles of `the to provide a`cascaded'high gain bidirectional amplifier' for two frequency'bands f1and fz. All of the .bandpass filters employed inthe circuit are tuned to-pass either offthe appliedl frequencies f1 or f2,-and to provideeiectivefshort-circuits double triode 39. A l

.kfIfhe anode of thefirst triode section'l ofthe Vsecond double triode39 is connected through a seventh ,fz bandpassfiilternetwork `to ,theygrid of` the second triode section of the first, double triode 1I. Theanodeofthe first triode section 'I of the first double triode "I isconnectedthrough ,aneighth ,f2 bandpass filter 61 -to` the .outputterminals for the second applied Vfrequency-f2.

n utflhefsixth, seventh and eighth f2 bandpassfilters 6'3,-$ 5,v 61 mayhave similar impedance characteristicsto theflfth f2 bandpass filter 5l, as described heretofore.` f

l Thus, in operationpsignalsofthe frequency `fi applied to the input yterminalsl of the firstl fi bandpass filter network 3 arelsuccessivelyamplified in the twofsectionsvoflv the first double triode 'I/ lv The,vamplified signals arel then applied throughv the second f1 filternetwork 23 and again 55- amplified through the Isections of the seconddouble triode' 39. v The signals then are passed through the third f1filter network 41, amplified further in the third double triode 5| andapplied through the fourth 'f1 filter 59, to the output bidirectionalamplierlof Figure-1 `are employed70 terminals for the first frequencyf1.

Similarly, 'signals'of the frequency f2 applied through the'fth f2filter 6I are amplified by the two sections'of 'the double triodeV 5|,passed through the sixthfi` filter network 53, amplified bytheftwoisections of *the second double triode 5.'A'bidirectionalg-amplifier forisignal--currents of vdifferent frequencyincluding first and second amplifying tubes each including a gridl'circuit and an anode circuit and having a-'common cath; odecircuitwhereby said tubes may besoperated asmutual bidirectional cathodefollowers, means tuned to pass currents of one of said frequencies andsubstantially to short-circuit currents of a different frequency foryapplying said isignal currents of said onefrequency to the grid circuit,of said first tube and fory short-circuiting currents of said differentfrequencyfbetween-said grid and cathode circuits of said first'tube,means tuned to pass currents of said different frequencyandsu-bstantially -to short-,circuit currents of said .Onefrequency forapplying said signal currents of said different frequency torthegridcircuit ofsaid second tube and for short-circuitingcurrents' ofsaidone frequency between grid and cathodecircuits' of said second tube,selectivemeans forderiving from said second tube amplified currents ofsubstantially only said one frequency, and additional selective meansfor deriving from` said first tube amplified currents of substantiallyonly said different frequency. j l i l6. A bidirectional amplifier fortwo frequencies including a pair of thermionic tubesleach having atleast grid and anode circuits and a common cathode circuit, a first'input circuit tuned to pass currents of one of said frequencies andsubstantially to short-circuit currents -of the yother of saidfrequencies, a second input circuit tuned to pass currents of said otherof said' frequencies and substantially to short-circuit currents of saidone of said frequencies, means for y applying currents of said onefrequency through said first input circuit to the grid-,cathode`circuitof Vone of said tubes, means for applying currents of said otherfrequency through-,said second input circuit tothe. grid-cathodecircuitof the other of said tubes, a first output circuit tunedsimilarly to said firstinput' circuitandconnected to the anode circuitof said other o'f said tubesya second output circuit tuned similarly to.said second input circuit andV connected tol-the anode circuit of saidone of said tubes, means :forgderiving amplified currents ofsubstantially only said first frequency from said first output circuit,and means simultaneously for ,-derivingamplified currents ofsubstantially only said second frequency from said second outputcircuit.

7. A bidirectional amplifier for I' two frequencies including a pairs-ofthermionic ,tubes each having at least` grid and anodesfcircuitsand lacommon cathode circuit whereby-'said tubes-may be operated asmutualbidirectionalcathodefollowers,` a first input circuit connectedacross the grid-cathode circuit -of one, of said tubes and tuned topasscurrents of one of said frequencies and substantially to short-circuitcurrentsof Athe other of said frequencies, a second vinput circuitconnected across the grid-cathode circuit of:A said other ofsaid tubesand tuned to pass currents of said other of said frequencies andysubstantially to short-circuit currents` of said one of: saidfrequencies, means for applying currents ofv said one yfrequency'through said first input circuit to said grid-cathode circuit of'saidonexof said tubes, means for applying-currentsy ofvsaid otherfrequencythrough said second input circuit to said grid-cathode circuit of vsaidother kof said tubes, a first output circuit tuned similalrly tosaidfirst inputfcircuit and connected to theanode circuit of said other ofsaid tubes, .asecond output circuit tuned similarly to said secondinput-circuit and connected to the anode circuit ofisaid--one of saidtubes, means for deriving amplified'cur-V rents of said first frequencyfrom said first output circuit, and means simultaneously for derivingamplified currents of said second frequency from said second outputcircuit. i

' 8. A lbidirectionalA amplifier for two frequencies including apairof'thermi-onic tubes each having at least gridfandanode circuits and acommon cathode circuit whereby said .tubes may beioperated las mutualbidirectional cathodefollowers, a first' input circuit connected acrossthe :grid-cathode circuit of. one of said tubes and tuned to passcurrents ofone ofv said frequencies andsubstantially toshort-circuitcurrentsofithe other of said frequencies, a second inputcircuit connected across thel grid-cathode circuit `of the other of saidtubes and tuned to pass currents of said other of said frequencies.` andsubstantially to shortcircuity currentsr ofsad one of f saidfrequencies, means for applying' currents' of said one frequencythroughA ysaid first` input 'circuit to saidgrid-cathode circuit of saidone ofsaid tubes, means for lapplying currents of said other frequencythrough said second input circuit .toysaid grid-cathode circuit ofsaidother of said tubes, avfirs-toutput circuit tuned simil-arly to saidfirst input circuit and connected across the anode-cathode circuiti ofsaid other of -said Itubessa second output circuit tuned similarly tosaid .second input circuit and connected across the anode-cathodecircuit of said one of said tubes, means for deriving amplified currentsof substantially only said first frequency from saidy first `'outputcircuit, and means lsimultaneously for deriving amplified currents ofsubstantially'only said second frequency from said second outputcircuit. l w L y a vv*9. A cascaded bidirectional amplifier comprising,`in combination, a'pair of amplifiers as described inclaim ,1 andincludingthird and lfourth amplifyingstubes each including `grid and.anode electrodes and having a'common cathode circuit whereby said thirdand fourthvtubes maybe operated asmutual .bidirectional cathodefollowers, means forfapplying amplified currents of said one frequencyderivedl from said second .tubeof the first of said pair of amplifierstothe grid of said third tube, means f-or applying amplified -currentsof .Said different frequency derived from said first tube of the otherof said pairof amplifiers to the grid of saidI fourth'tube,means'connecting the anode of said third tube tothe input ycircuit ofthesecond tube of the first of said pair of amplifiers, and mean-sconnecting the` anode `ofA said fourth tube to the input circuitof.theflrsttube of the other` of said pair OfamplifierS. i 4,

, 10.1A cascaded bidirectional amplifier comprising, in combination, apair'of amplifiers' as devscribed in claim 8 and including third andfourth amplifying tubes each including grid andanode electrodes andhaving a common' cathode circuit whereby said third and fourth tubes maybe oper'- ,ated as*` mutualbidirectional cathode followers,

means for applying amplified currents'of said one frequency derived from`said second tube of the first ofysaid pair of amplifiers to the grid ofsaid third tube,vmeans for applying :amplified currents `of saiddifferent frequency derived fromsaid first tube' of the other of saidpair ofamplifiers to the grid of said fourth tube, means connecting-theanode of said third tubeto the input circuit of the second tube ofth-efirst of said pair of amplifiers, and means connecting the anode ofsaid fourth tube to the input `circuit ofthe first tube 0f the other ofvsaidpair of amplifiers.,l f .as

1l. A reflex amplifier for modulated signals in cluding rst andsecondamplifying tube means Ieacl'i including grid and anode circuits andhaving a common cathode circuit whereby said amplifying tube means maybe operated as mutual bidirectional cathode followers, band pass `iiltermeans for applying said modulated signal to said amplifying tube means,a signal detector responsive to signals from said amplifying tube means,means for deriving the modulation component of said detected signals,means for applyingsaid modulation signal component to said amplifyingtube means in the opposite direction to said modulated signal, and meansfor utilizing amplied modulation signals derived in said opposite.direction from said amplifying tube means.

12. A bidirectional amplifier for signal Vcurrents of diner-entfrequency including first and second amplifying tubes each 4including aninput circuit and an output circuit and having a common coupling circuitwhereby said tubes may be operated as mutual cathode followers, meansfor applying signal currents of one frequency -to the input circuit ofsaid first tube, means for applying signal currents of a differentfrequency to the input circuit of said second tube, means for derivingfrom said second` tube amplified currents of lsaid one frequency, andmeans for deriving from said first tube amplified currents of saiddifferent frequency.

GEORGE C. SZIKLAI.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,020,813 Van Slooten Nov. 12,1935 2,185,367 Blumlein Jan, 2, 1940 2,327,248 Clase Aug. 17, 1943FOREIGN PATENTS Number Country Date 111,805 Australia Oct. 24, 1940

